1. Field of the Invention
The present invention relates to a process for producing a denaturated manganese dioxide catalyst for the hydration reaction of cyanohydrins. More particularly, the present invention relates to a process for producing efficiently manganese dioxide having a high catalytic activity for the hydration reaction of cyanohydrin in an aqueous phase.
2. Description of the Related Arts
The reaction for synthesizing an amide from a corresponding nitrile can be applied, for example, to the production of acrylamide from acrylonitrile or the production of methyl methacrylate from acetone cyanohydrin by way of .alpha.-hydroxyisobutyric acid amide. The development of an excellent catalyst for the synthetic reaction of amides starting from the corresponding nitriles is of great significance from the industrial standpoint.
It has already been well known that manganese dioxide is used as a catalyst for the synthesis of an amide by the hydration reaction of a nitrile, and a variety of methods for preparing the catalyst have been proposed. For example, it is disclosed in West Germany Patent No. 1593320 that manganese dioxide is prepared by reacting manganese sulfate and potassium permanganate in an equivalent amount at a temperature of 80.degree. C. in the presence of a little excessive amount of sodium hydroxide.
It is also disclosed in U.S. Pat. No. 4018829 that .delta.-type manganese dioxide is suitable for a catalyst in the hydration reaction of acetone cyanohydrin. The .delta.-type manganese dioxide, as described in Z. Anorg. Allg. Chem., 309 (1961), pages 10 to 14, is produced by the reduction of a manganese (VII) compound in the neutral to alkaline pH at a temperature of 20.degree. to 100.degree. C.
Moreover, as the production methods of amide compounds from nitriles, there are disclosed a method for utilizing a catalyst prepared by incorporating zinc into manganese dioxide which has been prepared from potassium permanganate and manganese sulfate in Japanese Patent Application Laid-Open No. 57534/1988 and a method for utilizing, as a catalyst, manganese dioxide which has been obtained by the reduction of an alkaline aqueous solution of potassium permanganese with hydrochloric acid in Japanese Patent Application Laid-Open No. 57535/1988.
Manganese dioxide prepared by the conventional methods as described above has problems that (1) a satisfactory yield of an amide as a target cannot be obtained when the manganese dioxide is directly used as a catalyst of the hydration reaction of cyanohydrins, (2) the activity of the manganese dioxide is insufficient and thus the amount of the catalyst to be used is increased, and (3) the catalytic activity is rapidly lowered during its repeated use. Accordingly, the aforementioned manganese dioxide catalyst has not yet been used in practice.
The present inventors have conducted research earnestly for the purpose of producing a manganese dioxide catalyst for the hydration reaction of cyanohydrins free from the aforementioned problems. Particularly, earnest research has been conducted on the requirements for preparing a manganese dioxide catalyst for the hydration reaction of cyanohydrins starting from a permanganate salt and a manganese (II) compound. As a result, it has been found that a denaturated manganese dioxide prepared with specified starting materials under a prescribed temperature condition exhibits an extremely high catalytic activity and a long lifetime as a catalyst. The present invention has been accomplished on the basis of such findings.